iOS: Apple's Find My Friends shares your location with other iOS users. If the other person isn't on an iPhone, Transitory.Me will share your location by email or text message.

Transitory.Me sends your current location as a link, so anyone can open it. It isn't the only app of its type, but you don't need to register or log in, which is nice—just download the app and share. Transitory.Me gives you control over how long your location is being broadcast, too. The link will autodestruct after a few minutes, but you can extend the time from the app—handy if the person hasn't responded yet.